1. Field of the Invention
The present invention relates to a connection arrangement, in particular an intermodulation-protected coaxial connection arrangement comprising a cable and a cable connection means, such as a coaxial connector, a lead-in unit or the like, fixed to the cable.
A connection arrangement of the above kind is applied in connections for the radio frequency range, for example in connections needed for filters, directional couplers and other equivalent components employed at a base station of a cellular network. These connection arrangements employ cable connection means, such as coaxial connectors or lead-in units.
The invention can e.g. be applied in connection with a coaxial connector to be attached to the outer wall of a housing encasing a filter, directional coupler or some other component or equipment. In particular, the invention involves coupling a coaxial connector to a cable within such a housing and to the wall of the housing. Another practical example is the connection of a lead-in unit to be attached to the outer wall of a filter housing or a housing for a directional coupler or other equipment to a cable brought inside the housing and to the housing wall, and the connection of the outer sheath of the cable to the housing wall. In these applications, the presently known connection arrangements and the methods for making them are such that the cable connection means, such as a coaxial connector or a lead-in unit, is attached directly to the wall by way of clamping means and/or a solder joint.
2. Description of the Prior Art
In connection arrangements for the radio frequency range, a significant problem is presented by intermodulation, which is induced as a combined result of several frequencies. Intermodulation may present a problem particularly at base stations for cellular networks, since several transmission frequencies are employed for different channels at one base station unit, thus causing intermodulation to occur. Intermodulation becomes a real problem when the frequency of the intermodulation is in the same frequency range as the receiving frequency of the base station. Even a small intermodulation will cause problems, as the difference between the transmit power and the intermodulation should be as high as 165 dB. The unit and value for the intermodulation is dependent on the smoothness of the component surfaces and the clamping force between the connected parts of the arrangement. In order to avoid intermodulation, the connection arrangements should be executed with particular care.
As stated previously, in the prior art connection arrangements the cable connection means, such as a coaxial connector or a lead-in unit, is directly coupled for instance to the outer surface of a filter housing. However, the interface between a coaxial connector and a filter housing, for example, cannot always be made so tight that no problem of intermodulation will occur. Particularly in filters of thin sheet construction, it is very difficult to form a sufficiently smooth connection surface against the connector in the wall of the filter housing. If, after completion of the connection arrangement, it is found in test measurement that the connection is not sufficiently tight and shielded against intermodulation, the entire filter must be discarded, which will naturally impair the output and economy of the manufacturing operation. The situation is similar when a lead-in unit is employed as the cable connection means. The prior art connection arrangements also have problems in replacement of the parts of the connection arrangement. Furthermore, the prior art connection arrangements are problematic in regard to their manufacture, as for instance a coaxial connector must be heated thereby to make it well soldered to the surface of the filter housing. It is obvious that such heating will adversely affect the connector structure and the connection surface of the connector, being seated against the filter casing. Heating of the connector will also adversely affect the connections already made between the cable and the cable connection means. These factors further impair the intermodulation suppression of the connection arrangement. In the known arrangements, problems will also be encountered in washing of the executed solder joint.
It is an object of the present invention to provide a novel connection arrangement avoiding the problems related with the prior art.